From the day i received my beagleboard rev. B7 i was
missing an easy way to use the digital video interface with a small
LCD screen. Many people seem to have
the same problem and often end up with big and expensive
adaptors. Further indication that this is a common problem comes from
the fact that the latest incarnation of the beagleboard includes a way
to directly interface to the OMAPs parallel video
interface. Unfortunatately this only provides 1.8v signals and still
needs a converter to interface to the 3.3v signals most raw LCD
use.

This page describes a cheap and simple yet flexible HDMI to
parallel 3.3v interface. This allows to connect most LCDs frames to
the beagleboard without any further interface required. I am using
this myself with some 7inch 800x480 displays which i am using to run
Angstrom Linux as well as
the maemo on
beagleboard project. I have used these lately for some work
on Meego.

The hardware

The hardware is rather simple and doesn't consist of much more than
the TFP101A
panel link receiver from TI. This chip directly outputs 3.3V
signals. The dvi2par routes these signals though 22R resistor arrays
to reduce reflections. The resulting signals can be fed directly into
a LCD screen as depicted below.

The schematic

The printed circuit board

Obtaining the parts

The main components is the TFP101A. I got mine as a free sample
from TI. All remaining parts have been bought in germany
from Reichelt
and Conrad. The part numbers
are:

Attaching the dvi2par to the display

The dvi2par is meant to directly interface to the LCD board. It can
be setup to either be run from >5V using the included voltage regulator.
Alternally it can be run directly from the 3.3V likely already present
to supply the dispay itself as seen in the image below.

The dvi2par mounted on top the displays old controller pcb

Also visible in this picture is the fact that only the upper 6
of the 8 color bits available on the dvi2par are being used. It's important
to make sure that the upper bits are being used if the display supports
less than 24 bit color depth. Also visible in the image is the fact that
a tiny wire goes from pin 8 of the TFP101A to some other parts on the
board is mounted on. Pin 8 carries the SCDT signal which indicates that
a valid signal has been detected in the input. In this example the signal
is routed to the backlight inverter and makes sure that the backlight is
only switched on if a valid HDMI signal is being received.

EDID/DDC support

The dvi2par also includes an optional i2c eeprom which is meant to
allow to use the dvi2par on hosts other than the beagleboard which
support to use a displays ddc/edid configuration. However, this part
has only been verified to be operational and to be usable on a
standard linux desktop PC. But since this part is not necessary on a
beagleboard, it isn't tested to all detail.

In order to use it, you need to build an EDID description for your
particular display using e.g. the Phoenix
EDID designer 1.3 (A windows software which runs fine in
wine). The output of this editor needs then to be programmed into the
dvi2par ddc eeprom. The jumper JP1 has to be set to enable writing the
eeprom. The i2c port of the hdmi connector then needs to be connected
to some linux controlled i2c hardware like e.g. my i2c-tiny-usb. Below
is an image of my i2c-tiny-usb based adptor used to write the ddc eeprom
on the dvi2par.

The archive contains some scripts (prom.sh) and a tool
(eeprom.c) to write the ddc data to the eeprom using the
depicted i2c-tiny-usb setup.

Spare displays for trade

I have two spare converted 7inch EEEPC screens i am willing to
trade for interesting parts like e.g. a beagleboard xm or
similar goods. These screen come with a little stand, and backlight
inverter. The displays are ready-to-run and only require a single 12V
1A power supply. I can provide a beaglebaord linux kernel configured
to match these displays. Send me an email if you are interested.